Hi Howie and thanks for reaching out!
Excellent question. The Events Calendar is our core plugin that allows you to publish events to your WordPress site in a calendar format.
Event Tickets extends the functionality of The Events Calendar so that you can add RSVP functionality to your even posts. Event Tickets–if you choose–can run on it’s own without The Events Calendar and it will add RSVP functionality to your WordPress pages and posts.
Event Tickets Plus extends Event Tickets so that you can sell tickets for your events posts when The Events Calendar is installed using the ecommerce platform (e.g. WooCommerce) of your choice. You can create tickets for events, set the number of tickets available for each ticket, and schedule the start and end dates for the tickets to be on sale.
So, to answer your question, there are two free plugins and one paid plugin you would need to get started selling tickets for events on your site. 🙂
Does this help clarify things a bit? Please let me know.
Cheers!
Geoff